Gas distributor for casting mold manufacture

ABSTRACT

A gas distributor nozzle adapted to be inserted within a mold cup for coating the cup includes an extended tubular element seated on the small end of a frusto-conical member. Conduit means through the extent of the of the member communicates said gas to the tubular element and to a plurality of apertures distributed about said member, each aperture extending upwardly and outwardly through the wall of said member towards said element.

United States Patent 1 Schweikert et al.

GAS DISTRIBUTOR FOR CASTING MOLD MANUFACTURE Inventors: Wilbur H. Schweikert; John S.

Mosier, both of Cincinnati, Ohio Assignee: General Electric Company,

Cincinnati, Ohio Filed: Jan. 9, '1973 Appl. No.: 322,166

Related U.S. Application Data Division of Ser. No. 195,284, Nov. 3, 1971, Pat. No. 3,731,650.

U.S. Cl. 239/567 Int. Cl. B05b 1/14 Field 61 Search ..1 18/47 495; 117/5.1, 5.2, 106 c,5.3,107.1;

[451 Nov. 6, 1973 [56] References Cited UNITED STATES PATENTS 3,070,982 1/1963 McGowan ll7/5.3 X 3,384,049 5/1968 Capita 1l8/49.5 3,398,718 8/1968 Pilloton... 118/48 3,417,733 12/1968 Makino 118/49 Primary Examiner-M0rris Kaplan AttorneyLee H. Sachs [57] ABSTRACT A gas distributor nozzle adapted to be inserted within a mold cup for coating the cup includes an extended tubular element seated on the small end of a frustoconical member. Conduit means through the extent of the member communicates said gas to the tubular element and to a plurality of apertures distributed about said member, each aperture extending upwardly and outwardly through the wall of said member towards said element.

3 Claims, 1 Drawing Figure fl an m v BACKGROUND OF THE INVENTION DESCRIPTION OF THE PREFERRED EMBODIMENTS I Precision casting molds of refractory materials have The high cemical reactivity between molten metals 5 long been produced by the well known investment cast within the mold. One method for making a mold suit: I

able for use in casting of titanium articles involves the deposition of a pyrolytic coating, one example of which is graphite, on the inner walls of such a mold. Such pyroltic graphite coating method and the resulting mold is described in U.S. Pat. No. 3,284,862 Schweikert, issued Nov. 15, 1966 and assigned to the assignee of the present invention.

One problem which has been recognized in the manufacture of such a mold is the proper introduction and application of gas from which the pyrolytic coating is produced. Such gas is first introduced on walls of the pouring cup and main sprue which first receive molten metal and on which a heaviercoating generally is necessary because of washing by the molten metal. In one example, under certain conditions, it was found that either blistering or pyrolytic graphite occurred in such areas or pyrolytic graphite was not properly formed due to turbulent gas flow or regions of gas stagnation.

SUMMARY OF THE INVENTION It is a principal object of the present invention to provide, for usein the apparatus for providing a pyrolytic coating on internal walls of a casting mold, a gas distributor for the mold cup and main sprue to avoid turbulent flow and gas stagnation in those areas during generation of the pyrolytic coating.

Another object is to provide apparatus including such a distributor to hold both the distributor and the mold during processing.

Theseand other objects and advantages will be more clearly understood from the following detailed description, the examples and the drawing, all of which are meant to be representative of rather than limiting on the scope of the present invention.

Briefly, the present invention, in one form, provides, in-apparatus for providing a pyrolytic coating on internal walls of the casting mold, a gas distributor for use in a mold cup and main sprue connected with the cup. The gas distributor comprises a gas receiving and distributing nozzle and a main sprue conduit. The gas receiving and distributing nozzle includes a gas inlet and a conduit port which communicates with a conduit inlet. Also includes is a nozzle wall, the outer surface of which is shaped generally to conform with the shape of the cup and which converges toward the main sprue. Through thenozzle wall are a plurality of gas discharge holes the outlets'of which direct the gas angularly along the cup in the direction of the main sprue in order to avoid turbulent flow and gas stagnation.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a sectional, partially diagrammatic view of the gas distributor of the present invention positioned within a casting mold for provision of a pyrolytic coating on the internal walls of the mold.

ing technique sometimes referred to as the lost wax process. For the manufacture of precision cast parts, such as those made of Ti or its alloys, it has been recognized that the interposition of certain pyrolytic coatings 0 between therefractory material and the'metal to be cast into the molds avoids reaction between the mold and the metal. In addition, use of a pyrolytic coating reduces contamination of the metal with coating material.

In practical casting manufacture, such precision casting molds are made to produce a plurality of articles in a single mold. Such a mold includes a pouring cup into which molten metal is first poured. The molten metal then passes into 'a main sprue or passageway from which it is passed into various other secondary passages which feed molten metal to that portion of the mold which is to produce the article. Thus, it is important that the pouring cup and main sprue be able to withstand washing of the molten metal in order to avoid reaction with the refractory material of which the mold walls are made.

It has been found that the present invention, positioned in the drawing in use in the generation of a pyrolytic coating on the walls of the precision casting ceramic mold, avoids the problems of coating blistering and powdering such as sooting in the case of pyrolytic graphite. In the drawing, the gas distributor of the present invention includes a gas receiving and distributing nozzle shown generally at 10 and preferably of graphite and a main sprue conduit shown generally at 12 and preferably of ceramic material such as dense aluminum oxide. The gas receiving and distributing nozzle has a gas inlet 14 and a conduit port 16 communicating with conduit inlet 18. The gas receiving and distributing nozzle 10 also includes a nozzle wall 20 having an outer surface 22 shaped generally to conform with the shape of mold pouring cup 24 and converging generally toward conduit port 16. A plurality of gas discharge holes 28-extend through nozzle wall 20. Each discharge hole has a hole outlet 30 which directs gas entering nozzle 10 through gas inlet 14 angularly toward the main sprue conduit 12 and along-the cup in the direction of the main sprue 26.

The main sprue conduit 12 communicates with the gas receiving and distributing nozzle 10 at the distributing nozzles conduit port 16 and the main sprue conduit inlet 18. Gas received by the main sprue conduit is discharged through conduit outlet 32 generally toward main sprue base 34, thus avoiding gas stagnation in that region.

Gas discharged from the gas distributor of the present invention through has discharge holes outlets 30 is directed in substantially laminar flow by outlets 30 along with surface of mold pouring cup 24 toward and into the interior of main sprue 26, toward main sprue base 34. In the area of the main sprue base, it mingles with gas discharged from conduit outlet 32 for distribution into other portions of the mold upon the walls of which the pyrolytic coating is to be deposited. For example, gas passes through secondary channels 36 into article mold cavity 38 in which the precision cast article is to be produced. The gas then is discharged through mold vents 40.

During processing of the mold to deposit a pyrolytic coating on its inner walls, the mold is placed in an ordinary heating enclosure (not shown) which can discharge gas emitted from mold vents 40. One such enclosure is shown in the above identified U.S. Pat. No. 3,284,862 as a graphite susceptor enclosing the mold. Surrounding the susceptor is an induction coil which, together with the susceptor, serves as a means to heat the mold and the gas through radiation. A graphite cover and a graphite base, shown partially in the drawing at 41, can be used to complete the enclosure.

Although the entire heated enclosure is not shown because the variety of ways in which such heating can be accomplished, the drawing does show a graphite mold and nozzle holder 42 which rests within such enclosure on base 41 and which is adapted to carry both the casting mold as well as the gas distributor of the present invention. Mold pouring cup lip 44 is located within holder first recess 46 to block gas discharged from outlets 30 from flowing around lip 44 and away from main sprue 26. In addition, nozzle wall rim portion 48 of nozzle wall 20 is located within holder second recess 50 to position outer surface 22 of nozzle wall 20 in proper spaced relationship with pouring cup 24. If desired, a sealing material 52, commonly used in the art, can be located in recess 46 and beneath holder 42 for addtional sealing. Holder 42 includes a holder gas inlet 54 which cooperates with nozzle gas inlet 14 and base gas inlet 56 to allow passage of gas from a source (not shown), into nozzle 10.

In one example, a ceramic shell mold having porous walls was made from commercially available materials by the lost wax process. After dewaxing, the mold was mounted on holder 42 on which has been mounted the gas distributor of the present invention, as shown in the drawing. The assembly thus provided was placed in a vacuum furnace apparatus, of the type described above, where it was heated in the range of l,900-2,200 F. During that time, acetylene gas was introduced through inlets 54 and 56 into gas inlet 14 of nozzle and subsequently discharged through gas outlets 30 and conduit outlet 32 into the cup and main sprue portions of the mold. Thereafter, unused gas passed through secondary channels 36 into article mold cavity 38 before excess gas was discharged from the mold through vents 40. The result was a continuous pyrolytic graphite coating on the internal walls of the mold without blistering or sooting on such critical surfaces as those of the pouring cup 24 and the main sprue base 34.

Thus, the present invention, which provides gas in laminar flow along critical internal wall surfaces of a mold on which a pyrolytic coating is to be deposited, avoids blistering and sooting through controlled gas flow and elimination of gas stagnation. Although the present invention has been described in connection with specific examples and embodiments, it will be understood by those skilled in the art, the modifications such as in conditions, materials, configurations, etc., and other variations which can be made within the scope of the present invention.

What is claimed is:

1. In apparatus for providing a pyrolytic coating on internal walls of a casting mold through use of a gas, a gas distributor for use in a mold cup and main sprue connected with the cup, the gas distributor comprising:

a gas receiving and distributing nozzle; and

a main sprue conduit open at a conduit inlet and an conduit outlet;

the gas receiving and distributing nozzle including:

a. a gas inlet b. a conduit port communicating the gas inlet with the conduit inlet;

0. a frusto-conically shaped nozzle wall defining said gas inlet and conduit port and converging toward said conduit port and seating the conduit inlet at the conduit port; and

d. a plurality of gas discharge holes through the nozzle wall, each hole extending upwardly and outwardly through said wall and communicating with said gas inlet.

2. The apparatus of claim 1 in which the gas receiving and distributing nozzle is graphite.

3. The apparatus of claim 2 in which the main sprue conduit is ceramic material.

* i III =8 

1. In apparatus for providing a pyrolytic coating on internal walls of a casting mold through use of a gas, a gas distributor for use in a mold cup and main sprue connected with the cup, the gas distributor comprising: a gas receiving and distributing nozzle; and a main sprue conduit open at a conduit inlet and an conduit outlet; the gas receiving and distributing nozzle including: a. a gas inlet b. a conduit port communicating the gas inlet with the conduit inlet; c. a frusto-conically shaped nozzle wall defining said gas inlet and conduit port and converging toward said conduit port and seating the conduit inlet at the conduit port; and d. a plurality of gas discharge holes through the nozzle wall, each hole extending upwardly and outwardly through said wall and communicating with said gas inlet.
 2. The apparatus of claim 1 in which the gas receiving and distributing nozzle is graphite.
 3. The apparatus of claim 2 in which the main sprue conduit is ceramic material. 